This proposal is a collaborative effect among New York City and Long Island researchers to determine whether environmental contaminants increase the risk of breast cancer among women on Long Island, New York. Concern about this issue among Long Island residents led to federal legislation mandating such a study. Recently, several studies suggest that certain environmental exposures, primarily some organochlorines (commonly used as pesticides), effect estrogen production under laboratory conditions, increase mammary tumors in animals, and many increase a woman's risk of breast cancer. Possible route through which organochlorine compounds (OCC) may effect breast cancer risk include estrogen metabolism. Further studies have linked residence near hazardous waste sites or chemical facilities with breast cancer risk. Although the exact exposures have not been identified, putative agents derived from such exposures may include polycyclic aromatic hydrocarbons (PAH), ubiquitous mammary carcinogens that are estrogenic in some in vitro test systems. The primary aim of the proposed study is to determine whether OCC (DDE, PCBs, chlordane) and PAH are associated with breast cancer risk among Long Island women. This investigation will be a five-year, population-based case-control study. Cases will be residents of Nassau and Suffolk counties who are newly diagnosed with primary breast cancer during a 12-month period. Cases will be identified through frequent review of pathology/cytology records. Population-based controls will be frequency matched to cases by 5-year age groups, and identified using random digit dialing and the Health Care and Finance Administration rosters. Completed in-home interviews are expected for 80% of eligible subjects (1,623 cases and 1,623 controls). About 60% of all respondents are expected to provide biologic specimens; for cases, specimens will be collected prior to treatment, whereas for controls, specimens will be obtained at the interview. Home samples of water, soil, and dust will also be collected among women who have resided in their homes for 15 years or longer. A random sample of blood and urine samples from 400 cases and 400 counts will be analyzed. Laboratory analyses include determination of OCC in blood, PAH-DNA adduct, and urinary markers of estrogen metabolism. The 650 home samples of soil, water, and dust will be assayed for pesticides and PAH. For all respondents, historic environmental exposure to these compounds will also be calculated using geographic modeling techniques, as well as self-reports of occupational and residential exposure. To estimate the association between breast cancer and exposure to OCC or PAH, adjusted odd; ratios and corresponding confidence intervals will be calculated using standard statistical methods. Effect modification by estrogen or carcinogen metabolism, and other factors (such as estrogen- receptor status, menopausal status, family history, or nutrition) will be explored where possible. The effect of established and suspected risk factors on breast cancer risk among Long Island women will also be assessed.